debug: remove the src/debugAdapter/.vscode/launch.json

[stamblerre]

This file appears to be a relic from when the main launch.json did not have any configurations for the debug adapter. This is no longer the case, so we should delete this file.

[eliben]

Related: #224

[hyangah]

@ramya-rao-a said it was used when launching both extension and debug server in debug mode was necessary in old days. Now, "Extension + Debug server" replaces it and works better.

I just verified it works as expected. (I could set breakpoints in both extension and debug server code in one vscode instance!)

We need documentation update here https://github.com/golang/vscode-go/blob/master/docs/debug-adapter.md#debug-vs-code-and-the-debug-adapter

cc @polinasok @stamblerre @quoctruong

[gopherbot]

Change https://golang.org/cl/238778 mentions this issue: src/debugAdapter: delete unused launch.json